1. Field of the Invention
The present invention relates to a display system mounted in an automobile vehicle. Particularly, the display system has a display unit and a reflector which are disposed in an instrument panel of the automotive vehicle. The display unit emits an image that is reflected by the reflector, and the image is projected on a windshield of the vehicle via an opening of the instrument panel. The display system superposes the image on a foreground seen from the vehicle such that a driver of the vehicle can see the superposed image and the foreground via the windshield simultaneously.
2. Related Art
Recently, a driver needs information increased in amount and in kind during operation of an automobile vehicle. A meter unit mounted on an instrument panel of the vehicle does not have a space enough to indicate all the information. Therefore, a projector-type display unit called as a head-up display (HUD) has been adopted so that an excess amount of the information can be projected on a windshield of the vehicle as a virtual image. The virtual image is superposed on a foreground which is visible through the windshield.
The projector-type display unit reflects an image projected by a projector on the windshield so that a driver can see the image. However, external rays such as sunlight enter the display unit through the windshield to reach the projector. Disadvantageously, infrared rays included in the external rays heat the projector, causing a problem that the heating and heat accumulation of the projector decreases a usage life of the projector.
To solve the problem, a prior-art head-up display unit has an infrared ray reflector (filter) disposed across a path of external rays to prevent breakdown of the indicator due to heating thereof. Such a prior-art head-up display unit is disclosed in Japanese Utility Model No. 64-35139 (Pages 4, 5, and FIG. 1).
FIG. 31 shows a general configuration of a conventional head-up display unit for a vehicle. Generally, such a head-up display unit is disposed in an instrument panel 1 arranged within a limited vehicle space. A virtual image S visible through a windshield 3 is to be apart more than 2 or 3 meters from a driver's eye I. Therefore, the head-up display unit has a reflector 4 like a concave mirror or a flat mirror, or a lens may be provided in place of the reflector to extend the distance from the virtual image to the driver's eye. However, external rays F such as sunlight enter the instrument panel 1 through the windshield 3 to reach a display device 5, causing the problem described above.
The head-up type display system indicates normal information including speed, telltale, and navigation. The head-up type display system also indicates an image of a foreground seen from the vehicle, which is taken by an infrared ray camera during the night.
The normal information of the display system is indicated desirably near a center of a driver's sighting angle. Furthermore, the indication must be positioned to have no ill effect on a normal vehicle operation for the driver. Moreover, the size of the indication (sighting angle) must be determined to be easily recognized but must not be too large to prevent the driver from recognizing a foreground of the driver's view.
The normal information is indicated with numerals, letters, illustrations, or telltales, while the camera-taken image is a moving picture in which a distant object is smaller than a nearer one. Therefore, the camera-taken image is necessary to be indicated with an increased scale to provide a desirable scale image to the driver, so that the image is larger than the indication of the normal information. That is, the head-up type display system has an optical system to enlarge the image as well as a function to alternatively indicate the normal information and the camera-taken image.
The head-up type display system needs to have a reflector 4 larger than a conventional one to enlarge a projected image. However, the larger reflector 4 collects more external rays that reach a display unit 5. Therefore, the conventional heat-absorbing or heat-reflecting element may not prevent undesirable heating of the display unit 5. A filter described in Japanese Utility Model No. 64-35139 or a hologram reflecting specified wave rays is not sufficient for preventing the heating of the display unit 5 because of the larger reflector 4.